Alcatel-Lucent 7450 Quality Of Service Manual page 761

High Scale Ethernet MDA Capabilities
In other systems, the downstream destination is represented as a scheduler in a tiered
hierarchical scheduler. This means that bandwidth is allocated on a per DSLAM basis without
regard to the class of packets being forwarded to that DSLAM. In this model, a set of
subscribers on one DSLAM receiving packets for a premium service are treated equally to
subscribers on other DLSAMs receiving packets associated with best-effort type services.
The intermediate destination secondary shaper solves the downstream overrun issue without
sacrificing class preference at the HSMDA egress port scheduler. All subscribers destined to
the same DSLAM have their queue groups mapped to the same egress secondary shaper. As
the scheduler services the queues within the groups according to their scheduler class, the
intermediate destination shaper is updated. Once the shapers rate threshold is exceeded,
scheduling for all queues associated with the shaper is stopped. Once the dynamic rate drops
below the threshold, the queues are allowed to be placed back on to the scheduler service lists.
By removing the queues from their scheduling context for a downstream congested DSLAM,
the port scheduler is allowed to fill the egress port with packets destined to other DSLAMs
without sacrificing class behavior on the port.
64 egress secondary shapers are supported which may be dynamically associated with an
egress physical port. Each HSMDA queue must be associated with a secondary shaper. By
default, a secondary shaper is created per physical port and all queues within a queue group
on the port are associated with the default secondary shaper. All default secondary shapers
will operate at the maximum rate and have no impact on queue scheduling. The hardware
supports mapping individual queues within a queue group to separate secondary shapers.
Based on the intended use case for secondary shapers, the provisioning model does not allow
queues within the same queue group to map to separate secondary shapers. Queues are
mapped to a secondary shaper on a queue group basis.
Quality of Service Guide 763